A definitive work detailing the history, the construction and use of airbrushes is "The Airbrush Book" by Seng-gye Tombs Curtis and Christopher Hunt published by Orbis Publishing Limited, London in 1980. This reference describes in detail the various types of airbrush past and present. As fine art tools, airbrushes are relatively delicate and, moreover, they are expensive. For example, conventionally, the nozzle and/or the needle (which control the release of paint) may be made of brass, stainless steel or a platinum alloy. They are easily damaged in that, to provide a different sized nozzle, to replace a damaged nozzle or needle, or for cleaning purposes, the airbrush must be disassembled, cleaned and reassembled. During reassembly, the needle must be inserted into the nozzle to exactly the correct extent to ensure a seal and to avoid damaging the nozzle.
FIG. 1 is a diagrammatic fragmentary cross-section of a known nozzle/needle combination.
The needle 10 has a tip of substantially conical shape sealingly fitting into a nozzle 12 projecting through the nozzle outlet so that, even when retracted during spraying, the end of the needle still projects beyond the nozzle outlet, the surface of the needle tip conveying paint to the exterior of the nozzle. The aperture in the nozzle 12 may be, for example, 0.2 mm. The diameter of the needle may taper from 1.5 mm to a point. Such a nozzle/needle combination can be seen in, for example, Swiss patent specification No. 99097 or U.S. Pat. No. 4,161,289. This combination provides better and more even delivery of paint than arrangements wherein, upon retraction, the needle lies wholly within the nozzle as shown, for example in U.S. Pat. No. 3,224,677 or U.K. specification No. 2,119,288.
As can be seen from the aforementioned Swiss patent specification No. 99097, the angle of taper is small so that, upon retraction of the needle, a considerable movement is necessary to give an appreciable change in the size of the annulus between the needle and the nozzle to vary the flow of paint. This is desirable so as to give greater control of paint flow. However, if the angle of taper of the needle is too small, the mechanical advantage is such that on moving to the closed position, the needle tip 11 tends, in use, permanently to spread the nozzle opening. The sealing may be reduced but also the airbrush no longer has the required control characteristics in the dispensation of paint. If the needle is bent, the paint will not flow evently. If the nozzle is bent or distorted, it will not locate concentrically with the needle or a surrounding air cap 13 and the airflow through the respective annuli between the needle and the nozzle and between the nozzle and the air cap will be uneven. Uneven flow of paint or of air gives rise variously to spatter, spitting, lack of focus or asymmetrical spray pattern. In an extreme case, of course, the nozzle 12 may well be split or cracked by the needle tip 11.
The needle and the nozzle are both relatively expensive items to replace but the errors produced due to the above-mentioned faults and to the time lost in correcting faulty artwork and/or in replacement or cleaning, can be more expensive.
Other forms of spraying equipment utilise concentric needle, nozzle and air cap arrangements and, to varying extents, suffer from the disadvantages above ascribed to airbrushes. The present invention relates equally to such other forms of spraying equipment.
An object of the present invention is the provision of an improved nozzle arrangement of low cost wherein the aforesaid disadvantages are minimised or overcome.